vkernel - Fix lockup with [v]kernel due to missing ipiq signal
* If the target ipiq has nothing but passively queued entries the target
cpu will normally just process the ipi's on the next clock interrupt.
However, if the originating cpu is forced to live-loop waiting for the
target to the drain the target may not be aware that it needs to drain
ASAP.
* The fix is for the originating cpu to ensure that an ipi interrupt is
sent to the target cpu before live looping.
* This appears to primarily effect vkernels.
Reported-by: ftigeot, tuxillo